What Men Grind Their Axes On.
Not many people realize that there is a special sort of whetstone for nearly every purpose. The proper sharpening stones or abrasives for use in various professions and trades and in household work are exhibited in the division of mineral technology in the older building of the United States National Museum, at Washington, D. C.
The exhibit shows specimens of the crude and partially prepared stones and the finished products ready for use, as well as a series of photographs which illustrate the operations of mining and preparing them.
Probably the first stone used for abrasive purposes was sandstone, a very widely distributed rock, and it is still used to-day. Its coarse grit and even grain first attracted attention, while the rough edge that it gave was all that was then required.
With the progress of the arts there began a search for various stones which could be used for sharpening objects of different sorts, so that to-day, not only sandstones, but mica schists, slates, and emery stones are used, besides several artificial compounds.
The hard, white, compact sandstones found near Hot Springs, Arkansas, are among the best whetstones known, equaling, if not surpassing, the Turkey stone, which for years has been considered one of the best. This Arkansas stone is known as novaculite, and occurs in two or three grades, intended for use with certain tools.
The hard, flintlike stone should be used only to sharpen instruments made of the very best steel, requiring very keen edges and points, such as those used by surgeons, dentists, and jewelers.
The other grades, although composed of the same ingredients, are more porous, the sand grains are not as close together, and a rougher edge is given to the sharpened tool. Because of their more porous nature, these stones cut faster, proving suitable for the finer-edged tools of carpenters, machinists, and engravers, and for honing razors.
Indiana and Ohio supply a whetstone made from a sandstone of a coarser grain than the novaculite of Arkansas, but nevertheless quite uniform. It may be used with either oil or water, and is useful for sharpening household cutlery, penknives, or ordinary carpenters’ tools. But since it is easily cut and grooved by hard and sharp steel, the fine instruments of dentists and surgeons should not be edged or pointed on this stone.
Scythe stones and mowing machine stones are practically all made from mica-schist rock found in New Hampshire and Vermont. These rocks are generally of a dark-gray color, and composed of very thin sheets of mica and quartz crystals interlaminated.
A simple experiment made about fifteen years ago led to the discovery of carborundum and crystolon. By heating a mixture of salt, sand, and sawdust, and powdered coke in an electric furnace, the variegated colored crystals of carborundum and crystolon were produced.
These crystals are extremely hard, cutting glass easily, and, in fact, almost any substance except the diamond.
Emery cloth and paper are very well-known commodities, but are little used to-day because the artificial abrasives are just as effective and cheaper. Experiments to obtain an artificial product having the main characteristics of emery resulted in the making of alundom and aloxite, both of which are shown in the museum series.